Comparison of the Sensitivity of Solid Phase MicroExtraction (SPME) and Stir Bar Sorptive Extraction (SBSE) for the Determination of Polycyclic Aromatic Hydrocarbons (PAHs) in Water and Soil Samples

Significance of the Topic

Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental pollutants originating from combustion processes. Their analysis at trace levels in water and soil is critical for regulatory compliance and protection of human and ecological health. Conventional methods rely on solvent-intensive liquid–liquid or solid-phase extractions, which are time-consuming, error-prone, and generate hazardous waste. Solventless sorptive techniques such as solid-phase microextraction (SPME) and stir bar sorptive extraction (SBSE) offer minimal sample preparation, lower contamination risk, and reduced environmental impact.

Objectives and Study Overview

This study compares the reproducibility and sensitivity of SPME and SBSE for the determination of 16 US EPA PAH compounds in water and soil extracts. Both techniques were evaluated using spiked aqueous standards (10 ppt to 4 ppb) and a NIST soil reference material.

Methodology and Instrumentation

Theoretical recovery calculations were performed using octanol–water partition coefficients and phase volumes (100 µm PDMS fiber vs. 10 mm, 0.5 mm PDMS SBSE Twister). Extractions used 10 mL samples containing 10 % methanol to prevent PAH losses to glass. SBSE employed a GERSTEL Twister and thermal desorption system (TDS/PTV) with splitless injection. SPME used a 100 µm PDMS fiber under optimized conditions: 35 °C agitation, 60 min extraction, 15 min inlet bakeout, and a 5:1 split desorption.

Main Results and Discussion

• Theoretical predictions indicated quantitative SBSE recovery for all PAHs except naphthalene; SPME favored only high-boiling PAHs.
• Reproducibility at low concentration: SBSE (100 ppt) achieved 4–28 % RSD; SPME (2 ppb) showed 7–79 % RSD, with poor precision for higher-molecular-weight PAHs due to incomplete desorption.
• Calibration linearity was good for both techniques over four-point ranges; SBSE detection limits ranged from 0.1 to 2 ppt, SPME from 0.3 to 84 ppt.
• Sensitivity of SBSE exceeded SPME by 20–80-fold, with practical detection limits about 100-fold lower in real chromatograms.
• Extracts of NIST SRM 1939 soil yielded 12–20 % RSD by SBSE; SPME lacked sufficient sensitivity for ppt-level soil extracts.

Benefits and Practical Applications

• SBSE offers enhanced sensitivity and lower detection limits without solvents.
• Both techniques streamline sample preparation and reduce contamination risk.
• SBSE enables direct analysis of water extracts from solid matrices, facilitating simpler soil monitoring protocols.

Future Trends and Potential Uses

• Development of thicker or longer Twister bars to further improve sensitivity.
• Investigation of alternative fiber coatings and advanced desorption liners.
• Integration with accelerated solvent-free soil extraction methods.
• Application to emerging contaminants requiring ultra-trace analysis.

Conclusion

SBSE demonstrates clear advantages over SPME for trace PAH analysis in terms of sensitivity, detection limits, and practical reproducibility, particularly at ppt levels. While SPME remains valuable for rapid screening of higher-boiling PAHs, SBSE is the preferred choice for comprehensive ultra-trace monitoring in environmental matrices.

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